Mercury removal from crude oil

ABSTRACT

A process for decreasing the level of elemental mercury contained in a crude oil at the well site by separating the crude oil stream into a gaseous hydrocarbon stream containing hydrocarbons, mercury and water, and a liquid hydrocarbon stream containing hydrocarbons and elemental mercury; removing mercury from the gaseous hydrocarbon stream in a mercury removal unit, thereby forming a treated gas stream; contacting a recycle gas stream comprising a portion of the treated gas stream with at least a portion of the liquid hydrocarbon stream for transfer of at least a portion of the elemental mercury contained in the liquid hydrocarbon stream to the recycle gas stream; thereby forming a mercury rich gas stream, and a treated liquid hydrocarbon stream; and passing the mercury rich gas stream, along with the gaseous hydrocarbon stream, to the mercury removal unit, is disclosed.

The present invention relates to a process for the removal of mercury from crude oil. In another aspect, this invention relates to a process for the removal of mercury from crude oil at the well site using produced gas.

Since the presence of mercury in crude oil can cause problems with downstream processing units, as well as health and environmental issues, there is an incentive to remove mercury from crude oil.

Therefore, development of an improved process for effectively removing mercury from crude oil before downstream processing into products would be a significant contribution to the art.

BRIEF SUMMARY OF THE INVENTION

In accordance with a first embodiment of the present invention, a process is provided including the following:

a) extracting a crude oil stream comprising elemental mercury, hydrocarbons and water from a crude oil well;

b) separating the crude oil stream into a gaseous hydrocarbon stream comprising hydrocarbons, mercury and water, and a liquid hydrocarbon stream comprising hydrocarbons and elemental mercury, and which can also include water;

c) charging a mercury-containing gas feed, including in part at least a portion of the gaseous hydrocarbon stream, to a mercury removal unit for removal of mercury from the mercury-containing gas feed, thereby forming a treated gas stream;

d) contacting a recycle gas stream comprising a portion of the treated gas stream with at least a portion of the liquid hydrocarbon stream for transfer of at least a portion of the elemental mercury contained in the liquid hydrocarbon stream to the recycle gas stream; thereby forming a mercury rich gas stream, and a treated liquid hydrocarbon stream; and

e) passing the mercury rich gas stream to the mercury removal unit as a portion of the mercury-containing gas feed.

In accordance with a second embodiment of the present invention, a process is provided including the following:

a) extracting a crude oil stream comprising elemental mercury, hydrocarbons and water from a crude oil well;

b) separating the crude oil stream into a gaseous hydrocarbon stream comprising hydrocarbons, mercury and water, and a liquid hydrocarbon stream comprising hydrocarbons and elemental mercury, and which can also include water;

c) removing water from a mercury-containing gas feed, including in part at least a portion of the gaseous hydrocarbon stream, prior to charging to a mercury removal unit for removal of mercury from the mercury-containing gas feed, thereby forming a treated gas stream;

d) contacting a recycle gas stream comprising a portion of the treated gas stream with at least a portion of the liquid hydrocarbon stream for transfer of at least a portion of the elemental mercury contained in the liquid hydrocarbon stream to the recycle gas stream; thereby forming a mercury rich gas stream, and a treated liquid hydrocarbon stream; and separating water from the liquid hydrocarbon stream; and

e) passing the mercury rich gas stream to the mercury removal unit as a portion of the mercury-containing gas feed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified schematic flow diagram presenting an embodiment of the present invention.

FIG. 2 is a simplified schematic flow diagram presenting an embodiment of the present invention.

FIG. 3 is a graphic illustration of a temperature vs. pressure curve, resulting from a simulation, above which temperature 90% mercury removal from a crude oil is predicted.

FIG. 4 is a graphic illustration of results from experiments concerning the removal of mercury from decane using methane as a sparging media.

DETAILED DESCRIPTION OF THE INVENTION

According to the first embodiment of the present invention, the process of the present invention will be described with reference to FIG. 1.

Referring to FIG. 1, crude oil is removed from a crude oil well by line 100 and is passed to separator 102 for separation into a gaseous hydrocarbon stream comprising, consisting of, or consisting essentially of hydrocarbons, mercury and water, which is removed from separator 102 by line 104, and into a liquid hydrocarbon stream: 1) comprising, consisting of, or consisting essentially of hydrocarbons and elemental mercury, or 2) comprising, consisting of, or consisting essentially of hydrocarbons, elemental mercury and water, which is removed from separator 102 by line 106. A mercury-containing gas feed, including in part at least a portion of the gaseous hydrocarbon stream, is charged to a mercury removal unit (MRU) 108 by line 110 for removal of mercury from the mercury-containing gas feed, thereby forming a treated gas stream, which is removed from MRU 108 by line 112. A recycle gas stream comprising a portion of treated gas stream from line 112 is charged to a contactor 114 by line 116 for contact with at least a portion of the liquid hydrocarbon stream charged to contactor 114 by line 106. Through such contacting, at least a portion of the elemental mercury contained in the liquid hydrocarbon stream is transferred to the recycle gas stream, thereby forming a mercury rich gas stream, which is removed from contactor 114 by line 118, and a treated liquid hydrocarbon stream, which is removed from contactor 114 by line 120. The recycle gas stream is charged to contactor 114 by line 116 below the location line 106 charges the liquid hydrocarbon stream to contactor 114. The mercury rich gas stream is removed from contactor 114 by line 118 at a location above the location line 106 charges the liquid hydrocarbon stream to contactor 114. The treated liquid hydrocarbon stream is removed from contactor 114 by line 120 at a location below the location line 106 charges the liquid hydrocarbon stream to contactor 114. The mercury rich gas stream is passed to the MRU 108 as a portion of the mercury-containing gas feed by lines 118 and 110.

According to the second embodiment of the present invention, the process of the present invention will be described with reference to FIG. 2.

Referring to FIG. 2, crude oil is removed from a crude oil well by line 200 and is passed to separator 202 for separation into a gaseous hydrocarbon stream comprising, consisting of, or consisting essentially of hydrocarbons, mercury and water, which is removed from separator 202 by line 204, and into a liquid hydrocarbon stream comprising, consisting of, or consisting essentially of hydrocarbons, elemental mercury and water, which is removed from separator 202 by line 206. Along with a mercury rich gas stream described later, the gaseous hydrocarbon stream is charged to a separator 207 wherein water is removed and exits separator 207 by line 208. The overhead gases leaving separator 207 by line 209 are charged to a mercury removal unit (MRU) 210 as a mercury-containing gas feed for removal of mercury from the mercury-containing gas feed, thereby forming a treated gas stream, which is removed from MRU 210 by line 212. A recycle gas stream comprising a portion of the treated gas stream from line 212 is charged to a contactor 214 by line 216 for contact with at least a portion of the liquid hydrocarbon stream charged to contactor 214 by line 206. Through such contacting, at least a portion of the elemental mercury contained in the liquid hydrocarbon stream is transferred to the recycle gas stream, thereby forming a mercury rich gas stream, which is removed from contactor 214 by line 218, and a treated liquid hydrocarbon stream, which is removed from contactor 214 by line 220. In addition, water is separated from the liquid hydrocarbon stream (and from the recycle gas stream, if water is present in such) and removed from contactor 214 by line 222. The recycle gas stream is charged to contactor 214 by line 216 below the location line 206 charges the liquid hydrocarbon stream to contactor 214. The mercury rich gas stream is removed from contactor 214 by line 218 at a location above the location line 206 charges the liquid hydrocarbon stream to contactor 214. The treated liquid hydrocarbon stream is removed from contactor 214 by line 220 at a location below the location line 206 charges the liquid hydrocarbon stream to contactor 214. Water is removed from contactor 214 by line 222 below the location line 220 removes the treated liquid hydrocarbon stream from contactor 214. The mercury rich gas stream is passed to the separator 207 along with the gaseous hydrocarbon stream by lines 218 and 204.

The crude oil stream of the present invention comprises, consists of, or consists essentially of a broad range crude oil. More particularly, the crude oil stream comprises hydrocarbons containing at least one carbon atom per molecule.

The gaseous hydrocarbon stream comprises, consists of, or consists essentially of hydrocarbons containing from about 1 to about 6 carbon atoms per molecule.

The temperature at which the crude oil stream is separated into the gaseous hydrocarbon stream and the liquid hydrocarbon stream is preferably at least about 50° C., more preferably at least about 60° C. The pressure at which the crude oil stream is separated into the gaseous hydrocarbon stream and the liquid hydrocarbon stream is preferably at least about 0.5 Bars, more preferably at least about 1 Bars.

The mercury removal unit has a fixed bed comprising any mercury sorbent material capable of removing mercury from gases.

The treated gas stream preferably comprises less than about 20 wt. % of the mercury contained in the mercury-containing gas feed, and more preferably less than about 10 wt. % of the mercury contained in the mercury-containing gas feed.

The treated liquid hydrocarbon stream preferably comprises less than about 50 wt. % of the elemental mercury contained in the liquid hydrocarbon stream, and more preferably less than about 20 wt. % of the elemental mercury contained in the liquid hydrocarbon stream.

The liquid hydrocarbon stream typically comprises at least about 10 ppb elemental mercury, and more particularly comprises at least about 200 ppb elemental mercury.

The recycle gas stream is contacted with the liquid hydrocarbon stream at a temperature in the range of from about 70° C. to about 300° C., preferably from about 150° C. to about 200° C., a pressure in the range of from about 0.5 Bars to about 15 Bars, preferably from about 1 Bar to about 10 Bars, and more preferably from about 2 Bars to about 7 Bars; and a gas to liquid ratio in the range of from about 50 to about 300 standard cubic feet of gas/bbl of liquid (SCF/bbl), preferably from about 100 to about 200 SCF/bbl.

The following examples are provided to further illustrate this invention and are not to be considered as unduly limiting the scope of this invention.

EXAMPLES Example 1

To test the idea, a simulation of the liquid/gas contactor was constructed using an equation of state thermodynamic prediction model for mercury partitioning between gas and liquid using data for elemental mercury in a commercially obtained crude oil blend. The results of the calculation are shown in FIG. 3, wherein the temperature of the crude oil is plotted against the pressure to achieve 90% removal of mercury from the liquid oil feed to the contactor. A gas to oil ratio of 80 SCF/bbl was used in the model.

This simulation shows that 90% mercury removal is achievable at the temperature and pressure conditions commonly present at the crude oil well site. That is, wherein the pressure of the Low Pressure Coalescer/Separator typically present at the well site (which is redeployed in the invention as a gas/oil contactor) ranges from about <1 to ˜3 Bars, and the reservoir temperature of high mercury crude oils is normally greater than about 150° C.

Example 2

An experiment was run to test the removal of Hg (elemental) from a hydrocarbon by sparging with a lighter hydrocarbon. Elemental mercury was dissolved in decane at about 1,300 ppbw. FIG. 4 shows the results of the experiment, plotting residual Hg in the decane vs. liters of methane sparged through the decane for two different runs, Runs 1 and 2.

A third experiment was run wherein, prior to adding the elemental mercury, the decane was water washed and passed over a silica gel column to remove trace levels of chloride, oxide or sulfur compounds that could, at the conditions of the experiment, oxidize the mercury and cause it to form non-spargable mercury compounds.

Also shown in FIG. 4 is a plot of the results of a theoretical calculation of the mercury removal process, and shows that the experimental results for Runs 1 and 2 are in good agreement with such, and that the experimental results for Run 3 is in excellent agreement with the theoretical calculations.

While this invention has been described in detail for the purpose of illustration, it should not be construed as limited thereby but intended to cover all changes and modifications within the spirit and scope thererof. 

1. A process comprising: a) extracting a crude oil stream comprising elemental mercury, hydrocarbons and water from a crude oil well; b) separating said crude oil stream into a gaseous hydrocarbon stream comprising hydrocarbons, mercury and water, and a liquid hydrocarbon stream comprising hydrocarbons and elemental mercury; c) charging a mercury-containing gas feed, including in part at least a portion of said gaseous hydrocarbon stream, to a mercury removal unit for removal of mercury from said mercury-containing gas feed, thereby forming a treated gas stream; d) contacting a recycle gas stream comprising a portion of said treated gas stream with at least a portion of said liquid hydrocarbon stream for transfer of at least a portion of the elemental mercury contained in said liquid hydrocarbon stream to said recycle gas stream; thereby forming a mercury rich gas stream, and a treated liquid hydrocarbon stream; and e) passing said mercury rich gas stream to said mercury removal unit as a portion of said mercury-containing gas feed.
 2. A process in accordance with claim 1 wherein water is removed from said mercury-containing gas feed prior to charging to said mercury removal unit in step c).
 3. A process in accordance with claim 1 wherein said contacting of step d) occurs in a vessel, and wherein said recycle gas stream is charged to said vessel below the location said liquid hydrocarbon stream is charged to said vessel, and wherein said mercury rich gas stream is removed from said vessel at a location above the location said liquid hydrocarbon stream is charged to said vessel, and wherein said treated liquid hydrocarbon stream is removed from said vessel at a location below the location said liquid hydrocarbon stream is charged to said vessel.
 4. A process in accordance with claim 1 wherein said gaseous hydrocarbon stream comprises hydrocarbons containing from about 1 to about 6 carbon atoms per molecule.
 5. A process in accordance with claim 1 wherein the temperature of said crude oil in step (a) is at least about 50° C., and wherein the pressure of said separation step (b) is at least about 0.5 Bars.
 6. A process in accordance with claim 1 wherein the temperature of said crude oil in step (a) is at least about 60° C., and wherein the pressure of said separation step (b) is at least about 1 Bars.
 7. A process in accordance with claim 1 wherein said mercury removal unit has a fixed bed comprising a mercury sorbent material.
 8. A process in accordance with claim 1 wherein said treated gas stream comprises less than about 20 wt. % of the mercury contained in said mercury-containing gas feed.
 9. A process in accordance with claim 1 wherein said treated gas stream comprises less than about 10 wt. % of the mercury contained in said mercury-containing gas feed.
 10. A process in accordance with claim 1 wherein said treated liquid hydrocarbon stream comprises less than about 50 wt. % of the elemental mercury contained in said liquid hydrocarbon stream.
 11. A process in accordance with claim 1 wherein said treated liquid hydrocarbon stream comprises less than about 20 wt. % of the elemental mercury contained in said liquid hydrocarbon stream.
 12. A process in accordance with claim 1 wherein said liquid hydrocarbon stream comprises at least about 10 ppb elemental mercury.
 13. A process in accordance with claim 1 wherein said liquid hydrocarbon stream comprises at least about 200 ppb elemental mercury.
 14. A process in accordance with claim 1 wherein said contacting of step d) occurs at a temperature in the range of from about 70° C. to about 300° C., and a pressure in the range of from about 0.5 Bars to about 15 Bars, and a gas to liquid ratio in the range of from about 50 to about 300 SCF/bbl.
 15. A process in accordance with claim 1 wherein said contacting of step d) occurs at a temperature in the range of from about 150° C. to about 200° C., and a pressure in the range of from about 1 Bar to about 10 Bars, and a gas to liquid ratio in the range of from about 100 to about 200 SCF/bbl.
 16. A process in accordance with claim 1 wherein said contacting of step d) occurs at a temperature in the range of from about 150° C. to about 200° C., and a pressure in the range of from about 2 Bars to about 7 Bars, and a gas to liquid ratio in the range of from about 100 to about 200 SCF/bbl.
 17. A process in accordance with claim 3 wherein said liquid hydrocarbon stream comprises hydrocarbons, elemental mercury and water; and wherein water is separated from said liquid hydrocarbon stream and removed from said vessel at a location below the location said treated liquid hydrocarbon stream is removed from said vessel. 